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    <script>
        //1. 求数组[2,6,1,7,4]里面所有元素的和及平均值
        let arr = [2,6,1,7,4];
        let sum= 0;
        for (let i=0; i<arr.length;i++) {
            //console.log(arr[i]);
            sum = sum +arr[i];
        }

        console.log('数组的和是' + sum);
        console.log('数组的平均数是' + sum / arr.length);
    </script>
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